Starting from the 80s in the twentieth century, with the development in micro-electro-mechanical-system (MEMS), miniaturization of some semiconductor devices, for example, various kinds of sensors, have been realized. Mass production has also been realized for producing these semiconductor devices and MEMS has become a main trend in future development.
In existing MEMS technology, an MEMS device is often formed from three stacked or bonded wafers. That is, three wafers are bonded or stacked together to form a stack structure and the stack structure is then diced to obtain the MEMS devices. In practice, the wafer in the middle has an arcuate or curved edge, and a great portion of side wafers might need to be reduced or thinned. To prevent the wafer in the middle from cracking during the wafer thinning process, the edge of the wafer in the middle needs to be trimmed. After the trimming process, gaps may be formed between the wafers around the edge of the wafer in the middle in the stack structure of three wafers. One or more wafers of the stack structure may be susceptible to cracking when, for example, during the thinning process of the top wafer to form the capping layer of the MEMS device, during the thinning process of the bottom layer to form the substrate of the MEMS device, or during the dicing process for dicing the thinned three-wafer structure. The cracking may affect the thinning and/or the dicing process, and may make it difficult or even impossible to obtain undamaged MEMS devices with small dimensions.
The disclosed methods and structures for forming MEMS devices to solve or improve, for example, the cracking problem during the fabrication process of MEMS devices and/or other problems.